This invention relates to a method and apparatus for the manufacture of clad tubes wherein a coating of a thermally deformable material is fused to the interior surface of a metallic tube.
Clad tubes are known in which a glass coating covers the interior of a metallic, for example steel, tube. According to methods known in the art, these clad tubes are formed by inserting a glass tube that is closed at one end into a steel tube, and placing the combination in a heating oven filled with an atmosphere resulting from the combustion of gas or heavy oil. The glass tube is softened by the heat, and then pressure is applied within the tube, causing the glass tube to inflate and fuse with the interior of the steel tube.
The initial set up for such a known fusing method is shown in FIG. 1, wherein 31 denotes a glass tube having a closed end 31a and a shaped end 31b. The shaped end is thermally deformed to form a nozzle to facilitate application of pressure to the interior of the softened glass tube. The glass tube 31 is positioned coaxially within a steel tube 2.
The known method of forming clad tubes has several drawbacks. In the first place, the glass tube 31 must be preformed to have a closed end 31a and a shaped end 31b. This necessitates the time consuming process of cutting a molded glass pipe to a selected length, reheating the two ends of the pipe and closing one end and shaping the other before the glass tube can be used in the process.
Secondly, the use of an oven to heat and soften the glass tube is inefficient, from the standpoint of both the time required to achieve softening and the difficulty of temperature control. Furthermore, clad tubes formed by this technique are prone to have bubbles which lower the utility of the coated tubing.
It is therefore an object of this invention to overcome these and other difficulties by providing a method and apparatus for forming clad tubes in which thermally deformable tubes that are open at both ends can be utilized in the manufacture of clad tubes.
It is a further object of the invention to provide a method and apparatus for manufacturing clad tubes in which an oven is not used to soften the tube of coating material.